WASHINGTON (Reuters) - A man killed in a crash last year while using the semi-autonomous driving system on his Tesla Model S sedan kept his hands off the wheel for extended periods of time despite repeated automated warnings not to do so, a U.S. government report said on Monday

The National Transportation Safety Board (NTSB) released 500 pages of findings into the May 2016 death of Joshua Brown, a former Navy SEAL, near Williston, Florida. Brown's Model S collided with a truck while it was engaged in the "Autopilot" mode and he was killed.

A Tesla Inc spokeswoman Tesla spokeswoman Keely Sulprizio declined to comment on the NTSB report. In 2016, the company said Autopilot "does not allow the driver to abdicate responsibility," however.

Brown family lawyer Jack Landskroner said in an email the NTSB's findings should put to rest previous media reports that Brown was watching a movie at the time of the crash, which he called "unequivocally false."

He added that the family has not taken any legal action against Tesla and was still reviewing the NTSB report.

The incident raised questions about the safety of systems that can perform driving tasks for long stretches with little or no human intervention, but which cannot completely replace human drivers.

During a 37-minute period of the trip when Brown was required to have his hands on the wheel, he apparently did so for just 25 seconds, the NTSB said in the report.

The report said the Autopilot mode remained on during most of his trip and that it gave him to a visual warning seven separate times that said "Hands Required Not Detected."

In six cases, the system then sounded a chime before it returned to "Hands Required Detected" for one to three second periods.

Tesla in September unveiled improvements in Autopilot, adding new limits on hands-off driving and other features that its chief executive officer said likely would have prevented the crash death. The updated system temporarily prevents drivers from using the system if they do not respond to audible warnings to take back control of the car.

The NTSB makes safety recommendations but cannot order recalls.

In January, the National Highway Traffic Safety Administration (NHTSA) said it had found no evidence of defects in the aftermath of Brown's death.

NHTSA said Brown did not apply the brakes and his last action was to set the cruise control at 74 miles (119 km) per hour less than two minutes before the crash -- above the 65 mph speed limit.

The agency said the truck should have been visible to Brown for at least seven seconds before impact. Brown "took no braking, steering or other actions to avoid the collision," the report said.

A Florida Highway Patrol spokesman said the truck driver was charged with a right of way traffic violation. He is due for a court hearing on Wednesday.

The NTSB report disclosed that the Tesla Model S uses a proprietary system to record a vehicle's speed and other data, which authorities cannot access with the commercial tools used to access information from event data recorders in most other cars.

For that reason, the NTSB said it "had to rely on Tesla to provide the data in engineering units using proprietary manufacturer software."